1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a refractory metal silicide layer on a semiconductor substrate made of a silicon material.
2. Description of the Related Art
A high degree of microstructuring has been pursued for a metal oxide semiconductor (MOS) field effect transistor (referred to as a MOS transistor in the following description) in accordance with scaling rules of semiconductor fabrication. A gate wiring width has been reduced, accordingly. With reduced gate wiring width, however, a short-channel effect increases and source and drain withstand voltage is reduced. Shallow impurity layers (source and drain regions) are effective for suppressing the short-channel effect and avoiding source and drain withstand voltage degradation. Formation of shallower impurity layers is desired. However, a sheet resistance of the source and drain regions increases as the regions become shallower. As a result, current drivability of the MOS transistor is reduced. That is, a response speed of the MOS transistor is reduced.
In order to overcome the problem, excimer laser annealing, for example, has been introduced wherein excimer laser is applied as heat treatment after ion implantation for forming source and drain regions. Excimer laser annealing is suitable for forming a shallow junction because only a shallow part of a surface of a substrate is heated in a short time with an application of excimer laser. In addition, excimer laser annealing allows the substrate to be heated to a high temperature. As a result, excellent crystallinity of the impurity layers is achieved, compared to rapid thermal processing (RTP). Source and drain regions with lower resistivity are thus formed. However, excimer laser annealing is still not sufficient for lower resistivity fabrication since a junction depth in the source and drain regions is contrary to a resistivity in each of the regions.
As another method of achieving a lower source and drain resistivity, a `salicide` (self-aligned silicide) process is disclosed in Chin-Yuan Lu, Janmye James Sung, Ruichen Liu, Nun-Sian Tsai, Ranbir Singh, Steaven J. Hillenius and Howard C. Kirsch, IEEE Transactions on Electron Device, vol. 38, no. 2, February 1991, pp.246-253. In the salicide process a metal silicide layer of a refractory metal such as a titanium silicide (TiSi.sub.2) layer is formed in a surface of an impurity layer. The salicide process, however, does not allow formation of shallower source and drain regions since current leakage must be avoided between the titanium silicide layer and a semiconductor substrate. If a shallower impurity layer is formed, the titanium silicide layer goes through the impurity layer to the semiconductor substrate. Therefore the salicide process is accompanied with the problem of current leakage between the titanium silicide layer and the semiconductor substrate while a lower resistivity of source and drain regions is achieved. It is thus required to form an impurity layer deep enough for preventing the titanium silicide layer from penetrating the impurity layer. As described so far, each of the excimer laser annealing and the salicide process has its merits and demerits for achieving a lower resistivity of source and drain regions.
In order to form a titanium silicide layer which is satisfactorily thin but does not penetrate an impurity layer of shallow source and drain regions, a method has been introduced to form a thin film of titanium (Ti) of 20 nm or less over an impurity layer to be reacted with a silicon substrate so as to form the thin film of titanium silicide. However, a layer of lower resistivity is hard to achieve with higher activation energy when forming the thin film of titanium into titanium silicide as described in Nikkei Microdevice ed., Technological White Paper of Low Power LSI: A Challenge to 1 Milliwatt, pp. 218-222. Heat treatment under a higher temperature is required for obtaining a thin film of titanium silicide with a low resistivity. However, titanium silicide coheres due to the high temperature heat treatment, which prevents formation of a titanium silicide layer of a low resistivity.
An application of a cobalt silicide (CoSi.sub.2) layer has been proposed as a refractory metal silicide layer without cohesion as described in, for example, K Goto et al., IEDM '95 (Tech Dig.) pp. 449-452. In this method, too, it is desired to reduce current leakage by suppressing a spike locally growing in a cobalt silicide layer. A spike growth in a cobalt silicide layer is frequently seen when the cobalt silicide layer is formed through a layered film (TiN-Co). In contrast, a spike growth is hardly seen when the cobalt silicide layer is formed through a single layer of cobalt (Co). However, a cobalt silicide layer of lower resistivity cannot be obtained through a single layer of cobalt.
As described so far, a junction in an impurity region is required to be much shallower due to microstructuring of a device, which is accompanied with a much thinner silicide film. Therefore the problems described above are commonly found in conventional device structures.